1. Field of the Invention
The present invention relates to a servo information recording method and apparatus for a disc drive, and more particularly, to a method and apparatus for exactly compensating for a track zero position when copying a reference servo pattern in a disc drive adopting a reference servo track copying method.
2. Description of the Related Art
Commonly, hard disc drives (HDDs), a kind of data storage device, reproduce data recorded on a disc or write data on a disc using a magnetic head. According to the trend for high capacity, high density, and compactness of the HDDs, the number of bits per inch (BPI), which denotes the recording density in a disc rotating direction, and the number of tracks per inch (TPI), which denotes the recording density in a disc diameter direction, has been increased. Accordingly, a more elaborate operation mechanism is required for the HDDs.
An HDD includes a head disk assembly (HDA) and a printed circuit board (PCB) assembly, which is involved in writing and reading of information by electrically controlling the HDA. As shown in FIG. 1, the HDA includes a head 16 for writing or reading information, a disc 12 having recorded thereon information from the head 16, a spindle motor (not shown) for rotating the disc 12, an actuator arm 24 for moving the head 16, a voice coil motor (VCM) 30, and an inner crash stop (ICS) 36 and an outer crash stop (OCS) 38 for limiting the displacement of the actuator arm 24. Here, the ICS 36 and the OCS 38 are bumpers for preventing the head 16 from moving to locations at which servo information of the disc 12 is not recorded.
The servo information is necessary to perform position control of the head 16 on the disc 12 so that data can be read/written from/on a desired position of the disc 12. Writing the servo information on the disc 12 is called a servo track write (STW) operation.
An increase of recording density of HDDs results in an increase of the number of tracks, and a ratio of the time for the STW operation to the time for the entire operation is gradually higher.
To improve this problem, a method of not writing servo information of discs after the discs are assembled with HDDs but directly assembling discs on which servo information is recorded with HDDs is developed, and this STW method is called an offline STW method.
However, in the offline STW method, since a rotational axis of a disc is not equal to the center of servo tracks, since a track center of a disc is not equal to a track center of another disc, or since centers of tracks on a disc surface are not the same, the servo control performance is decreased.
An STW technology developed to solve this problem is called a reference servo track copying method. As shown in FIG. 2, in this method, after one reference disc on which servo information is recorded and blank discs on which the servo information is not recorded are assembled with an HDD, an offline servo track writer writes the same reference servo pattern on all disc surfaces operated at the same time along with tracing servo tracks written on the reference disc.
Accordingly, in a reference servo track copying method according to the conventional technology, a reference servo pattern is copied by harmonizing a reference track zero position with a copy track zero position as shown in FIG. 5A.
As one of problems generated due to the reference servo track copying method, beginning positions of reference servo tracks are irregular due to disarrangement of heads of the offline servo track writer or occurrence of concentricity, and thus the head 16 may collide against the ICS 36 or the OCS 38 after assembly.
According to the conventional technology, after track zero compensation information is sought in a separate operation after servo pattern writing and is stored in a specific position on a memory or a disc, the track zero compensation information is read and loaded in random access memory (RAM) when an HDD is initialized, and thus an actual track zero position should be adjusted in every track seek procedure using the track zero compensation information. Accordingly, an access time is longer.
In addition, in a case where the track zero compensation information is stored in flash memory, if a PCB assembly is replaced, the track zero compensation information cannot be recognized. Also, in a case where the track zero compensation information is stored at a specific position of a disc, if a reading characteristic is unstable when an HDD is initialized, the track zero compensation information cannot be read, or a drive warming-up time is longer.